Conventional antennas used in a wireless local area network (LAN) system or a ultra wide band (UWB) radio system depend on the characteristics of a frequency band used in that system, and have the directional property of a relatively wide angle. For that reason, those antennas also have a wide range of available applications and acceptable environments, and are expected to become widespread in the future. However, a demand for the increased transmission rate of a radio communication has been more and more increasing in the recent years, and a radio communication system using a millimeter waveband or the like which is capable of ensuring a further ultra wide band has been studied (IEEE 802.15.3c).
The millimeter waveband has such advantages that the linear property is high, and an influence of interference is low, as well as an advantage of being capable of ensuring confidentiality, as compared with a microwave band. Up to now, the millimeter waveband has been used in some fields including communications among buildings, a video transmission system for a home television, or the like, as an alternative to a wire communication, and “ARIB STD-T69”, “ARIB STD-T74”, or the like has been established as a standard.
There has been proposed a conventional radio communication systems, which has a control station with a plurality of antennas, and a plurality of terminal station (for example, refer to Patent Document 1). On a control station side of the conventional radio communication system, signals from the plurality of terminal stations are sequentially received by the plurality of antennas, the qualities of the signals received by the respective antennas are measured, and an antenna that has received a signal highest in quality is used for a communication with the terminal stations.    Patent Document 1: JP 7-135675 A